1,720,992 research outputs found
A New Method For Efficient Time-Domain Simulation Of Power Electronic Circuits
No full textIn this paper a method for fast time-domain simulation of power electronic circuit with switches is described. The method is based on transient windows analysis joined by DC analysis on reduced circuits at the switching instants. It shows that the proposed approach provides the same results of standard analysis methods with a consistent reduction of the iterations required
Analisi di piccolo segnale per convertitori PWM ac/dc e dc/ac con la tecnica del frequency-shift
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A feature extraction unsupervised neural network for an environmental data set
No full textEnvironmental data sets are characterized by a huge amount of heterogeneous data from external fields. As the number of measured points grows, a strategy is needed to select and efficiently analyze the useful information from the whole data set. One efficient way of obtaining the validation-compression of data sets is the adoption of a restricted set of features that describe, with an assigned accuracy a subset of the whole data set. One characteristic feature of the environmental data is time dependency: in the medium and long term they are not stationary data sets. The aim of this work is to propose a feature extraction technique based on a new model of an unsupervised neural network suitable to analyze this kind of data. The paper reports the results obtained utilizing the above extraction and analysis procedure on a real data set on chemical pollutants. It is shown that the proposed neural network is able to identify correctly human and/or meteorological effects in the environmental data set
SOM-Based Approach for the Analysis and Classification of Synchronous Impulsive Noise of an In-Ship PLC System
No full textThe interest in wideband data transmission over power line communications has increased rapidly. This technology offers a convenient and inexpensive medium to transmit data, reducing the number of cables. This advantage is particularly appealing in many fields, like the railway, naval, and aeronautical ones. Nevertheless, several problems have to be faced to obtain a high data rate. In particular, the presence of noise makes the transmission difficult, degrading the quality of received signals and prohibiting the full application of these communication frameworks. In this paper the behaviour of an in-ship powerline communication system is analyzed in the presence of synchronous periodic impulsive noise. Such noise is modelled at source and its effects on the transmission of wideband signals are evaluated by means of a simulation circuit model. The obtained results allow to identify the characteristics of the channel and the critical conditions due to noise. Subsequently, an unsupervised technique based on principal component analysis and fuzzy c-mean classifier detects the presence and classifies the specific noises. Numerical results show that the proposed approach enables to achieve this target accurately under different operating conditions, proving to be an effective tool to enhance the performances of the considered technology
Non-Destructive Technique for Defect Localization in Concrete Structures based on Ultrasonic Wave Propagation
No full textConcrete structures require periodic inspections and quality control to assess their structural integrity. For this task several methodologies based on different technologies have been previously proposed. In particular, Non-Destructive Techniques, based on the use of ultrasonic wave propagation, have revealed attractive due to the possibility to perform reliable assessments of concrete structures. In this paper a method exploiting ultrasonic propagation characteristics is proposed. The aim of the method consists of determining the position of a defect by the computation of flight times related to signals reflected by anomalies in the structure. Such computation is based on a preliminary classification of defect positions that combines a genetic algorithm for a feature selection and a statistical approach for classification. The performances of the proposed method are evaluated in a specific case study, showing satisfactory numerical results, which show that this approach can be used to identify the position of small sized defects
AOI based Neurofuzzy System to Evaluate Solder Joint Quality
No full textSurface Mount Technology is extensively used in the production of Printed Circuit Boards due to the high level of density in the electronic device integration. In such production process several defects could occur on the final electronic components, compromising their correct working. In this paper a neurofuzzy solution to process information deriving from an automatic optical system is proposed. The designed solution provides a Quality Index of a solder joint, by reproducing the modus operandi of an expert and making it automatic. Moreover, the considered solution presents some attractive advantages: a complex acquisition system is not needed, reducing the equipment costs and shifting the assessment of a solder joint on the fuzzy parts. Finally, the typical low computational costs of the fuzzy systems could satisfy urgent time constrains in the in-line detection of some industrial productive processes
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